What are the symptoms of Klinefelter syndrome (KS)?

KS symptoms are different for every person. In most cases, symptoms do not show up until the teen or young adult years. In other cases, symptoms show up during infancy or childhood.


  • Delayed motor skills, such as sitting up or walking
  • Speech delays
  • Undescended testicles (when one or both testicles have not dropped into their usual position outside of the body)


Physical symptom and signs

  • Taller than average height
  • Longer legs, shorter torso, and wider hips than other boys
  • Increased breast tissue (gynecomastia)
  • Low muscle tone (hypotonia)
  • Low energy levels

Social development symptom and signs

  • Challenges with social interactions
  • Challenges with learning in school, such as with reading, writing or math
  • Attention deficits (ADD)

Teens and young adults

  • Low or no sperm production
  • Infertility
  • Low sex drive
  • Incomplete or delayed puberty (change from childhood to adulthood)
  • Less facial or body hair
  • Small, firm testicles
  • More belly fat and less muscle than usual
  • Anxiety and depression
Rev. 9/2018